The third space is a vague concept that describes an abstract idea, more so, a "utopian" metaphor for a space that is not visible or palpable. Clarity on its meaning -let alone its operationalization- is still limited. In addition, there is a lack of clarity regarding how partnerships in Teacher Education (TE) can attain and foster the third space and address the challenges that arise from its implementation. Nevertheless, the concept continues to provoke researchers, practitioners, and policy-makers who advocate for expanding the use of the third space as a model for school-university partnerships and an alternative to support professional development in TE. 

In attempting to understand the promising third space concept, its implications for TE, and the establishment of more sustainable and effective partnerships, this study presents the results of a scoping review of the literature. Therefore, the aim is to conceptualize the third space from the introduction of the concept in the field of TE in 2010 by Kenneth Zeichner and identify relevant themes for TE around the world. The following research question guided the search: How has the academic literature conceptualized the third space of professional practice in ITE from 2010 to 2019?

Growing interest internationally, especially in the USA, the UK, and Australia (Le Cornu, 2016; Lemon et al., 2018; Bernay et al., 2020) but also within the European countries (Lillejord & Børte, 2016; Wiedenhorn & Janssen, 2020), points to creating and fostering collaborative and sustainable partnerships. Improving "quality" -another vague concept in the educational sciences- in the training of prospective teachers is a crucial objective of school-university partnerships that need to collaborate and create opportunities for the pre-service teachers to connect different knowledge sources. This study helps us understand the characteristics and challenges of the third space concept in TE worldwide. The focus on the local context of Norway serves as an illustration of how the concept moves beyond the stage of theoretical conceptualization into policy and practice.

In educational sciences – as much as in the social sciences- it is common to use vague concepts to denote the abstract ideas and phenomena we study. The use of such vague concepts rapidly expands and become "buzzwords" that are difficult to operationalize and for which there is no real consensus on its meaning. As Blikstad-Balas (2014) argues, recognizing the vagueness of concepts should not necessarily mean that our research efforts are not precise; instead, "the recognition that our research terms are paradigmatically vague is an advantage…it should change how we approach such terms" (p. 535). Hence, we ought to be aware of the vagueness of the concepts we use, the pitfalls associated with them, and the analytical inferences we make from empirical data. 

The third space is one of these vague yet popular concepts in teacher education. The third space is a concept borrowed from post-colonial theory (Homi K. Bhabha, 1994). An effort to explain this concept within TE would be that the third space is a metaphor that describes a participatory approach where participants collaborate and co-construct knowledge about teaching and professional practice. The concept also describes how partnerships for professional practice can be developed in less hierarchical ways where the schools and TE institutions relate in more equal terms in the professional development of prospective teachers. 

This study's implications are relevant for TE programs in Europe as it explores the third space concept in establishing partnerships that foster a more democratic relationship between schools and TE institutions. As professional development is a crucial discussion in the field, the conceptualization of the promising third space can help us understand how to best support pre-service teachers. 

This scoping review of the literature draws on the five-step framework that Arksey & O'Malley (2005) developed, which was Levac et al. (2010) later enhanced. We also followed the guidelines for conducting scoping reviews by Peterson et al. (2015). We use a scoping review because it allows us to reveal the vagueness of the third space concept and provide a synthesis of how contemporary literature has used the concept to define professional practice in TE. We extensively searched peer-reviewed articles and book chapters in eight databases and two scientific journals. The inclusion criteria determined the time range (2010-2019), the type of publication (articles and book chapters), and the content (use of the third space in professional practice in TE) After removing repeated and irrelevant studies, 65 were identified for the screening process. The data extraction from these 65 studies included title, abstract, aim, findings, and conclusions. Later these studies were ranked on a scale from 1 to 3. On this scale, articles numbered 3 were highly relevant. The ones marked with 2 were in doubt, and those with 1 were discarded. To define the relevance of the ones marked with 2, the authors reviewed each study independently, and a consensus was met as to which ones should be included and which ones not. The final scoping review included 36 studies. During the analysis, we coded, classified, and categorized obtained from the 36 studies from which we developed descriptive codes and relevant themes of the conceptualization of the third space.

As expected, conceptualizing a vague concept such as the third space is not straightforward. The findings approximate a consensus of its use and confirm the growing interest of the third space in TE. Up to the present day, two years after the literature search, new studies have surfaced, such as Chan, 2020; Laughlin, 2021; and Green, 2021, among others. Hence the relevance of researchers' efforts to operationalize the concept based on empirical research and innovations that can potentially expand our knowledge of how to build partnerships and how to aim towards the third space in TE. The studies address the third space as a construct where partners' identities are in constant negotiation and where possibilities to do epistemic work surface. The third space aims to support less hierarchical structures and relationships among participants. Thus, studies identify the potential of the third space to construct school-university partnerships that are both more equal and intertwined. However, the studies also find that partnerships in the third space are riddled with tensions and challenges regarding participants' relationships, power struggles, and constraints of development and sustainability. Hence, studies point out that despite challenges, partnerships in the third space are not merely organizational constructions but seek to combine academic and experience-based knowledge and different epistemologies for mutual professional development. Further, the literature defines the vague third space concept in terms of three main themes. First is the negotiation of identities; this refers to the constant movement of partners in and across the institutional and epistemological boundaries, performing hybrid roles. The second refers to the intersection of epistemologies, which highlights new ways in which pedagogical possibilities are allowed by the collaboration among partners. The third space also facilitates the interconnection of knowledge sources, which is further enhanced by using digital environments to foster the third space.

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